1. Field of the Invention
The present invention relates to a vibrational actuator. More specifically, it relates to a vibrational actuator that generates vibrational energy by causing vibration of an elastic body and obtains a drive force by extracting this vibrational energy as an output.
2. Description of Related Art
Japanese Laid Open Patent Publication No. S59-96881 discloses a vibration wave motor that generates a progressive vibration wave (hereafter referred to as a progressive wave) at a drive surface of an elastic body as a piezoelectric member expands/contracts. At the drive surface, an elliptical motion attributable to the progressive wave occurs and a mover that becomes pressed in contact with the wave front of the elliptical motion is thus driven. By mounting such a vibration wave motor, which retains a high torque even at a low rotation rate in a certain type of drive device, the need for gears at the drive device may be eliminated. Thus, advantages such as elimination of gear noise and an improvement in the positioning accuracy are achieved.
If the diameter of a vibration wave motor is reduced for purposes of miniaturization, the torque generated thereat (torque=tangential force×diameter) becomes smaller, resulting in a smaller output (output=torque×rotation speed) of the vibration wave motor. This means that the rotation speed of a more compact vibration wave motor with lower torque needs to be raised. However, such an increase in the rotation speed may lead to a problem of abnormal noise.